Biogenic Fe(III) minerals: From formation to diagenesis and preservation in the rock record

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…Despite the consensus amongst workers that the precursor phase during the sedimentation of IF was most likely Fe(III)-oxyhydroxides (e.g., Konhauser et al, 2002;Kappler et al, 2005;Posth et al, 2014;Sun et al, 2015) or an Fe(III)-Si gel (e.g., Percak-Dennett et al, 2011;Zheng et al, 2016), there is renewed interest in possible alternative phases that may have influenced or been important for BIF sedimentation. These alternative authigenic phases include dominantly Fe(II) or mixed-valence phases, such as greenalite and various "green-rust" phases.…”

Sedimentology of the ∼3.3 Ga upper Mendon Formation, Barberton Greenstone Belt, South Africa

“…Sawicki et al (1995) demonstrated microbially-mediated precipitation of siderite in a biofilm, which suggests that siderite could have precipitated in situ. Siderite could also have formed through reactions of Fe(II) or Fe(III) oxyhydroxides with organic matter during diagenesis (Köhler et al, 2013;Posth et al, 2013;Posth et al, 2014). The combined effects of diagenesis, metamorphism, and surface oxidation make it difficult to isolate any one primary composition and the original ironbearing phases probably included a range of mineralogical compositions.…”

“…There are a number of abiotic and biologically-mediated mechanisms through which hydrated Fe(III) or mixed valence oxyhydroxides (e.g. "green rust", Zegeye et al, 2012) could have formed, most of which involve oxidation of Fe(II) in the water column by free oxygen or through microbial metabolic activity (Posth et al, 2014). Rasmussen et al (2014Rasmussen et al ( , 2015aRasmussen et al ( , 2015b suggested that deposition of Fe(II)-rich precursors to iron-bearing clays like ferrosaponite was a significant mode of reduced iron deposition in Archean environments.…”

Limited Zn and Ni mobility during simulated iron formation diagenesis

“…It is important to note, however, that these are all secondary minerals, and that the primary iron precipitates probably comprised ferric oxyhydroxides, such as ferrihydrite (Fe(OH) 3 ) (see Bekker et al, 2010 for review). Although the actual mechanisms of Fe(II) oxidation remain uncertain, they appear to have been biologically mediated (e.g., Posth et al, 2013aPosth et al, , 2014Pecoits et al, 2015). The organic biomass deposited with Fe(OH) 3 would subsequently serve as a reductant during diagenesis and metamorphism (e.g., Perry et al, 1973;Konhauser et al, 2005;Johnson et al, 2008;Craddock and Dauphas, 2011).…”